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GOLD
30
MODERN MINING
August 2016
Above:
One of the vertical
mills in the fine grind section
of the FFG circuit (photo:
Arthur Tassell).
Right:
Another view
of hydraulic mining by
DRDGOLD. The hydraulic
mining method is the main
‘mining’ method used by
DRDGOLD although front-
end loaders are used to
reclaim a small proportion
of the company’s tailings
resource – specifically, the
sand dumps which resulted
from the early ‘stamp
milling’ process.
research by DRDGOLD revealed that pyrite
particles, containing some 40 % of the gold
entering the Brakpan facility, were not respond-
ing as well as expected to the CIL process used
at the plant.
“We decided that the best way to improve the
recovery would be to introduce fine grinding to
liberate the gold within the pyrite particles. But
you can’t fine grind 1,8 Mt of material a month,
as the energy costs would be prohibitive. So
we’ve also reintroduced flotation – a process
used by Anglo American when it originally
commissioned the Brakpan plant but which
was subsequently discontinued – to separate
out the sulphides contained in the incoming
feed. The new flotation and milling sections,
together with a small dedicated leaching plant,
constitute the FFG circuit.”
Schoeman added that while a 0,03 g/t
increase in gold recovery might seem small, the
huge volumes processed at Brakpan meant that
this marginal improvement translated into sig-
nificant additional gold production of around
50 kg or 1 700 ounces a month.
Although the FFG or high-grade circuit came
on line in January 2014, it operated for less
than three months before DRDGOLD decided
to suspend operations as it was not delivering
the outcomes expected and, in addition, was
having a negative impact on the low-grade CIL
circuit. At the time, Pretorius described the
decision to take the FFG offline as the biggest
and most difficult decision he had had to take
during his tenure as CEO of DRDGOLD.
By September 2014, DRDGOLD had com-
pleted an analysis of the problems and
optimised the circuits and was confident
enough to reintroduce one stream of the three-
stream FFG circuit, with generally positive
results. It followed up in January 2015 by
restarting the other two circuits. The result was